This invention relates to a method of producing belts for use in high speed heavy-duty radial tires.
In general, belts for constituting high speed heavy duty tires, for example, tires for aircraft extend beyond shoulders of the tires in order to prevent standing waves and the like. If such belts are formed into cylindrical shapes by means of cylindrical forming drums in the conventional manner, ends of the belts in width directions of the tires are pushed radially inwardly by inner surfaces of vulcanizing molds in vulcanization to cause slacks and wrinkles thereat. In order to avoid this, midways of the belts in the width directions are radially outwardly expanded relatively to the ends of the belts to cause configurations of the belt to follow inner surfaces of the vulcanizing molds as much as possible.
In producing the belts in this manner, for example, as shown in FIGS. 1a and 1b, a first wide belt ply 2 and a second narrow belt ply 3 are applied onto a cylindrical forming drum 1 one after another during centering of these plies 2 and 3. Thereafter, ends of the first belt ply 2 in width directions are folded to form a lamination 4 and then the lamination 4 is transferred from the forming drum 1 to a forming drum 5 having larger diameters at a mid portion than diameters at ends in axial directions. Then, diameters of the forming drum 5 are enlarged to expand in radial directions the substantially mid portion of the lamination 4 in axial directions. Third belt plies 6 in layers are then attached on the lamination 4. In such a method, however, shearing forces would occur between the first and second belt plies 2 and 3 in width directions of tread during the deformation of the lamination 4. Therefore, these belts do not precisely deform following the outer circumference of the forming drum 5. Moreover, even if the desired deformation is carried out, there is a risk of reinforcing cords and rubber being separated. During forming, furthermore, the lamination 4 must be transferred from the forming drum 1 to the forming drum 5. The transfer of the lamination 4 from drum 1 to drum 5 lowers the working efficiency and makes difficult the centering of the lamination 4 relative to the forming drum 5.
In order to solve these problems, the following method will be considered. First and second belt plies 12 and 13 are attached to a forming drum 11 similar to the forming drum 5 above described, while centering the belt plies 12 and 13. Thereafter, ends of the first belt ply 12 are folded to form a lamination 14. Third belt plies 15 in layers are then attached onto the lamination 14, while the belt plies 15 are being subjected to tensile forces, so that the lamination 14 is deformed to follow the outer circumference of the forming drum 11.
In such a manufacturing method of belts, however, when the first belt ply 12 is folded, there are slight clearances between folded positions 16 of the first belt ply 12 and the forming drum 11. Therefore, the first belt ply 12 is not restrained at the folded portions 16. Thus the first belt ply 12 is likely to be folded at positions out of the predetermined folded positions 16. Moreover, at the commencement of application of the third belt plies 15, the lamination 14 is scarcely restrained by the forming drum 11 so that the lamination 14 is deformed by attaching the third belt plies 15 onto the lamination 14. As a result, the third belt plies 15 tend to be unintentionally shifted and tend to be attached to the lamination 14 out of the desired positions.